Speaking in Kiev, Sen. John McCain called Saturday for the United States to provide long-term military assistance to Ukraine, saying it is “the right and decent thing to do,” as reports surfaced that Russian troops had traveled farther north into Ukraine from Crimea.

McCain was part of a bipartisan delegation of U.S. senators who traveled to Kiev ahead of Sunday’s secession referendum in Crimea. The White House and U.S. allies in Europe have denounced the referendum as unconstitutional and illegal because Russian troops have essentially taken over the southern Ukraine peninsula.

McCain also had strong words for President Barack Obama in an op-ed appearing in The New York Times. He called for the President to take actions to restore the United States’ credibility and strength around the world.